What would we do if we discovered a large asteroid on course to impact Earth? While highly unlikely, that was the high-consequence scenario discussed by attendees at an Oct. 25 NASA-FEMA tabletop exercise in El Segundo, California.

The third in a series of exercises hosted jointly by NASA and FEMA -- the Federal Emergency Management Agency -- the simulation was designed to strengthen the collaboration between the two agencies, which have Administration direction to lead the U.S. response. "It's not a matter of if -- but when -- we will deal with such a situation," s

Something about the scenario mentioned doesn't quite square up for me. The scenario was a simulated impact date of September 20th, 2020, with astronomers being able to determine with 100% likelyhood that impact would occur by May of 2017. And then they say:

"While mounting a deflection mission to move the asteroid off its collision course had been simulated in previous tabletop exercises, this particular exercise was designed so that the time to impact was too short for a deflection mission to be feasible"

Really? 3 years is too little time? For a gravity tractor, definitely, but I'd like to think somebody would put a nuclear warhead on a rocket.

I ran some numbers assuming a nuke equivalent to 8 MegaTons of TNT (mass about 2 metric tons) which is on the upper edge of this plot:

and (assuming 1% of the warhead's energy is converted to kinetic energy) I calculated how big a dV this might cause in various sized impactors (assuming spherical comets/asteroids) and how long that dV would need to cause an Earth width deflection:

Pretty rough working I know, and I'm sure it's been done more precisely elsewhere, but we know a Falcon 9 can put DSCOVR in Sun-Earth L1 in 100 days and could be ready in under 6 months. SE-L1 is 1.5 million Km from Earth (or about 20 hours for a comet moving at 20km/s).

So to deflect a 250m impactor that they're talking about, you'd need the nuke to meet the rock at least that far away from Earth (probably more depending on trajectory). A falcon 9 could certainly put a 2 ton payload at least that far out in 4 months.

Maybe it would take another 8 months to get through the legal implications of putting a nuke on a rocket, but honestly, if that was the only way to do it, I'd like to think it would happen. In any case, I'm not sure I see why it need take much longer than 18 months?

It doesn't really help us if we had a dinosaur-killer comet coming in from outside the ecliptic like comet sliding spring, but for <1km impactors with >2 years warning, surely we could make it work...

One would hope that ~ 2 years would be enough to launch a nuclear warhead to deep space, but the question will be how much of a deflection that will give. Several warheads may be needed, or the deflection may not be enough to avoid an impact, just change the impact's location.

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One would hope that ~ 2 years would be enough to launch a nuclear warhead to deep space, but the question will be how much of a deflection that will give. Several warheads may be needed, or the deflection may not be enough to avoid an impact, just change the impact's location.

That's kind of the point of Mikelepage's chart... he runs some calculations that I would call conservative (but others may differ) for various sized items showing how much lead time is needed to move the thing by 1 earth diameter (and thus a near miss)... arguably 1 earth diameter may not be enough, dunno about you but I'd rather go for 10 diameters if we're talking about anything with any mass (and possible fragments in similar trajectories)

I think maybe you might look at the chart and then discuss which assumptions you think are wrong?

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"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

You could use a small nuke and a large nuke for a deflection attempt. Have a near surface detonation of the small nuke (about 15 kT yield) to kick up and vaporized material from the impactor. Then send in the large nuke to detonated within the debris cloud of the small nuke. Should be more kinetic energy transfer than with just detonating a nuke alone.

That's kind of the point of Mikelepage's chart... he runs some calculations that I would call conservative (but others may differ) for various sized items showing how much lead time is needed to move the thing by 1 earth diameter (and thus a near miss)... arguably 1 earth diameter may not be enough, dunno about you but I'd rather go for 10 diameters if we're talking about anything with any mass (and possible fragments in similar trajectories)

Yes, we probably could get more than 1% yield converted to kinetic energy, but as you say, we also would like a bigger deflection than one Earth diameter. Depending on the trajectories/gravitational interactions, one Earth D may not even be enough to stop impact. So yes, I'm not sure whether it is conservative on the whole or not.

From what I understand, it is preferable to do "stand-off" denotations some distance from the comet nucleus to prevent too much "spread" of the resulting fragments. The further away you detonate the nuke, the less yield you convert to dV, but also the safer it is.

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Taking it a step further, my next thought experiment is roughly how much lead time you might need to deflect a dinosaur killer (12km) comet. It would almost certainly be a comet, coming in from outside the ecliptic plane, because by this stage we know where most of the bigger asteroids are.

From my previous chart, needing at least 293 days lead time on an impactor moving at 20 km/s means the deflection point would be as much as 3.3 AU out from the sun, and if it was more than 10 degrees out of the plane (as is likely) we would need a gravity assist at Jupiter just to get the payload out to it before it was too late. For the sake of argument I'm just assuming Jupiter is in the right place at the right time for what we need. The New Horizons Pluto probe (400kg) went direct to Jupiter in 13 months.

Comet sliding spring was coming in at an inclination at 129 degrees (or 51 degrees retrograde) so if we're being generous it's going to take at least another 13 months to get to a deflection point 51 degrees below the plane, at ~5.5 AU. The deflection force could afford to be somewhat less that far out, which means the payload mass could be somewhat less. But we would probably still need a Falcon Heavy class launcher to put a 1-2 ton payload on a direct trajectory to Jupiter, whipping out of the ecliptic plane to meet the incoming comet and create a ~0.5m/s deflection.

In a reasonable best case scenario, by the time you factor in approvals/preparing the rocket, we would need 3 years or so lead time before the deflection date, which in turn would be 477 days before impact. => we need at least 5 years lead time all up to have a realistic chance at deflecting a dinosaur killer (12km) comet.

In a reasonable best case scenario, by the time you factor in approvals/preparing the rocket, we would need 3 years or so lead time before the deflection date, which in turn would be 477 days before impact. => we need at least 5 years lead time all up to have a realistic chance at deflecting a dinosaur killer (12km) comet.

Dunno about you but I would strongly prefer we send a fleet of deflectors, not just one, for that sort of happening... send dozens on short headings.. the later ones can divert if the deflection was enough from the first few. Not a place to skimp, IMHO.

"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

One would hope that ~ 2 years would be enough to launch a nuclear warhead to deep space...

Looking at the launch logs .. No. Only with completely unprecedented and prompt global collaboration maybe, but this is launching nukes to space, so even that would be doubtful.

I have no doubt it could be /attempted/ in that time given the importance. But Blackstar is right: this is about evacuation planning, and this is just the story that goes along with it.

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Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

You're missing the point of the exercise: it's an evacuation exercise. In other words, assuming that much warning time, what kind of evacuation is realistic?

I understand that. My point is, if 3 years is enough time to launch a nuclear deflection mission, then your evacuation planning is completely upended by the fact that the majority of people will be thinking: "let's wait and see how the deflection mission goes before we really get serious about evacuation".

You're missing the point of the exercise: it's an evacuation exercise. In other words, assuming that much warning time, what kind of evacuation is realistic?

I understand that. My point is, if 3 years is enough time to launch a nuclear deflection mission, then your evacuation planning is completely upended by the fact that the majority of people will be thinking: "let's wait and see how the deflection mission goes before we really get serious about evacuation".

Perhaps you should contact the people at NASA and FEMA and tell them that they are doing their work wrong. You can do that through an email or a letter.

I understand that. My point is, if 3 years is enough time to launch a nuclear deflection mission, then your evacuation planning is completely upended by the fact that the majority of people will be thinking: "let's wait and see how the deflection mission goes before we really get serious about evacuation".

Perhaps you should contact the people at NASA and FEMA and tell them that they are doing their work wrong. You can do that through an email or a letter.

Please don't put words in my mouth.

Crucial word in my post was "if". My presumption is that NASA/FEMA are doing their work right. But as I said, in my opening post, it doesn't quite square up for me: The stated premise of the exercise is that 3 years was too short a lead time, yet some BOE math suggests as little as 18 month lead time might be okay for a nuclear option.

At least one other person thought I was being somewhat conservative, so what am I missing? Perhaps NASA/FEMA are being extra conservative and assuming the nuke option is off the table? In any case, an interesting topic for discussion here, I thought, was the question of whether 3 years really too short a lead time to mount a planetary defence mission.

3 years is too short to launch a planetary defense mission that you'd have high confidence of succeeding. Thus the need to start evacuation preparations.

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Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

The delta V is given by vaporising one side of the asteroid with gamma rays and x-rays. But this can only be done to a certain depth - probably a couple of metres.

To cover the right surface area, the warhead will need to explode above the surface, so more than half the energy will be lost. Or could the gamma rays be channelled?

For a metallic asteroid, might a neutron bomb be more effective?

In any event, it's likely that several small bombs will be more effective than one large bomb.

Using a penetrating nuclear warhead - Hollywood style - might then be left as a last resort.

Back in 2009 when we (the National Academies) did our study on NEOs and surveying and mitigating strategies I had a couple of people on our committee who had modeled the effects of nuclear explosions on an asteroid. To be honest, I ended up confused. There were some people who claimed that "we don't know" how the nuke would actually affect an asteroid, and there was at least one guy who had access to nuclear weapons modeling data who seemed very confident that they understood it. I came away confused by all that, suspecting that there just was not enough data on the composition of asteroids--particularly any specific asteroid that you needed to move--to know with high confidence what the effects would be.

However... a few years ago I ran into a guy who worked at one of the national labs who was modeling the effects of a nuclear explosion on an asteroid. This was unclassified research, and I think he told me that at least one other group at another national lab was also modeling the subject. This is all going on memory, but I think he said that the basic effects of a nuke in terms of energy transfer are unclassified and you don't need special secret software to model it. (You do need that for some other aspects of nuclear explosions, although I don't know what. I believe I've read that it is possible to shape the direction of energy transfer from a nuke so that you can maximize the effects in one direction. But I don't know about that. If so, I'm sure all that modeling and simulation stuff is classified.)

Anyway, my long bit of rambling is that I think there are people who are pretty confident that they understand the energy transfer. But maybe that is false confidence. If you really had to do this, I think you'd probably want to send a bunch of them and you'd want to measure the effects of the first one in order to maximize your later shots. You'd probably want to do that over a relatively longer period of time.

But... that's not really what this thread is about. The thread is about emergency preparedness for a big one hitting.

New White House document deals with the threat of Near Earth Objects (NEOs).Credit: NASA

The White House has released a National Near-Earth Object Preparedness Strategy Ė a document developed by the Interagency Working Group (IWG) for Detecting and Mitigating the Impact of Earth-bound Near-Earth Objects (NEOs) (DAMIEN).

As detailed in the strategy, there are seven strategic goals that underpin the effort to enhance the Nationís preparedness to NEO impacts:

Enhance NEO Detection, Tracking, and Characterization Capabilities. Objectives include: developing a capability roadmap to inform a strategy for investing in both U.S. and foreign abilities for detection, tracking, and characterization; improving observation capabilities for more complete and rapid observation of the entire population of NEOs; and updating existing observatories with capabilities to improve characterization assessments.

Improve Modeling, Predictions, and Information Integration. Objectives include: ensuring that adequate modeling capabilities are developed for each topical need, especially for modeling NEO trajectories to reduce orbit uncertainties and predicted impact effects; determining what outputs are required by whom; and establishing an organizational construct to coordinate the development and dissemination of modeling results.

Develop Emergency Procedures for NEO Impact Scenarios. Objectives include: promoting a collaborative national approach to defend against, mitigate, respond to, and recover from a NEO impact event; and developing coherent national and international communication strategies to facilitate NEO impact preparations.

Establish NEO Impact Response and Recovery Procedures. Objectives include: establishing national and international protocols to efficiently respond to a NEO impact, whether in deep ocean, coastal regions, or on land; and facilitating international cooperation and planning to recover from a NEO impact in a timely manner with minimal disruption.

Leverage and Support International Cooperation. Objectives include: building international support and policies for acknowledging and addressing the potential Earth impact of a NEO as a global challenge; fostering consultation, coordination, and cooperation channels and efforts for the planning for, impact emergency preparedness before, and response to a NEO impact; increasing engagement with the international community on observation infrastructure, data sharing, numerical modeling, and scientific research; strengthening international coordination and cooperation on NEO data and National Near-Earth Object Preparedness Strategy analyses; and promoting a collaborative international approach to preparedness for NEO events.

Establish Coordination and Communications Protocols and Thresholds for Taking Action. Objectives include: coordinating the communication of detected impact threats within the U.S. Government, as well as with other governments, media, and the public; developing a set of thresholds to aid U.S. decisions in whether to implement deflection or disruption missions; developing decision flowcharts for NEO hazard scenarios incorporating bench-marks and decision thresholds; and developing protocols for international interactions regarding NEO impacts outside of U.S. territory.

These seven high-level goals and associated objectives outlined in the Strategy are intended to support a collaborative and Federally-coordinated approach to developing effective policies, practices, and procedures for decreasing the Nationís vulnerabilities associated with the NEO impact hazard.

This chart is actually quite useful if you look at it closely. What you can see is that nearly 100% of the "global" threat asteroids have been detected. The percentage of lower impact threats detected then drops off (that blue line).

I wonder if it is possible to overlay the expected outcome of something like a prime observation phase for NEOCam and see how much that would affect detection. NEOCam is roughly equivalent to the requirements in the George E. Brown Act, so it would probably cover a really good percentage into the "Region" category.